Recuperative heat exchanger



2 Sheets-Sheet 1 Filed Jan. 16, 6

INVENTOR EBERHARD TIEFENBACHER Lab/ ATTORNEYS Oct. 21, 1969 E. TlEFENBACHER RECUPERATIVE HEAT EKCHANGER Filed Jan. 16, 1967 2 Sheets-Sheet 2 INVENTOR EBERHARD TIEFENBACHER ATTORNEYS United States Patent 3,473,604 RECUPERA'HVE HEAT EXCHANGER Eberhard Tiefenhacher, Ludwigsburg, Germany, assignor to Daimler-Benz Aktiengesellschaft, Stuttgart-Unterturkheim, Germany Filed Lian. 16, 1967, Ser. No. 609,557 filaims priority, application Germany, Jan. 18, 1966, D 49,161 Int. Cl. FZSf 3/00 "US. Cl. 165-166 12 Claims ABSTRACT OF THE DISCLOSURE A recuperative heat-exchanger formed by a plurality of undulated plates in which two plates each are combined into a unitary plate structure with the troughs and crests thereof aligned to form a plurality of channels in a first direction coinciding with the direction of alignment, and in which each unitary plate structure is displaced by half a wavelength of the undulation with respect to the nextadjacent plate structure or structures to form thereby a plurality of closed channels of undulated configuration and extending in a second direction perpendicular to the first direction; to close off the sides of the second-mentioned undulated channels, structural terminal parts are used which may be in the form of undulated bars having rectilinear end portions with respective ends bent back upon themselves. The fixed connection of the various place structures may be efiected by inserting solder in the form of paste or foil at the mutual abutment places and subsequently oven-soldering the entire heat-exchanger assembly.

BACKGROUND OF THE INVENTION The present invention relates to a recuperative heatexchanger whose heat-exchanging mass consists of individual plates between which extend flow passages or paths mutually directed in a cross-like manner, of which the flow paths or channels extending in one direction are traversed by a liquid or gaseous hot medium, for example, by the exhaust gas of an internal combustion engine, and of which the flow paths or channels extending in the other direction are traversed by a liquid or gaseous colder medium, for example, the combustion air for an internal combustion engine.

Recuperative heat-exchangers are known in the prior art which consist of many plane or fiat plates arranged mutually parallel at the same distances for the formation of flow passages extending mutually crosswise, of which alternatively and sequentially the one flow passages or paths extend in the one direction and the other flow passages or paths perpendicularly thereto. In order to fix or secure the individual, very thin-walled plates at their required mutual spacing or distance from one another and to increase the heat-exchanging surfaces, inserts in the form of undulated plates are provided between the individual plates whose undulations extend perpendicularly to the flow direction of the two media. Bars or strips are arranged as spacer supports between the individual plates at the edges thereof which are rigidly connected with the plates and close off laterally the flow paths (German Patent 949,953).

Furthermore, cross-current plate-type heat-exchangers are known in the prior art in which, in lieu of undulated inserts, the individual plates are provided with indentations or embossments which assure the mutual spacing of the individual plates and simultaneously enlarge the heat-exchanging surfaces within the individual flow passages. Also in these last-mentioned heat-exchangers terminal bars or strips are arranged as lateral boundary of the individual flow paths at the edges of the plates or in 3,473,6fi4 Patented Oct. 21, 1969 ice the alternative, the plates are provided with bent-up rims for this purpose (German Patents 822,400 and 1,142,618).

The disadvantages of heat-exchangers of the aforementioned constructions reside in that heat stresses occur alternately between the individual flow passages as a result of the very thin-walled plates, on the one hand, and the relatively thick-walled bars or strips on the other, due to the heat difierences existing during operation, which heat stresses lead to crack formations. Additionally, with the known heat-exchangers, the cross-sectional ratio between the flow paths for the hot medium and the flow paths for the cold medium is influenced adversely because the effective cross section of the flow paths on the exhaust gas side is reduced as a result of the indentations provided for the mutual support of two adjacent plates which are necessary in particular by reason of the lower pressure on the exhaust gas side. However, this is contrary to the requirement that the hot exhaust gas requires a larger volume than the cold air. In order to satisfy this requirement the spacings between the individual plates have to be increased on the exhaust gas side with the heat-exchangers of the known prior art, which in turn adversely afiects the structural volume and makes necessary two different thicknesses for the terminal strips or bars.

SUMMARY OF THE INVENTION The purpose of the present invention is to avoid the disadvantage of the known constructions and to create a recuperative heat-exchanger reliable in operation to a high degree and combined with a simplified and less expensive construction both from a structural as well as a manufacturing point of view, in which additionally by simple measures, the cross-sectional ratio between the flow paths of the two media participating in the heat exchange can be changed.

The underlying problems are solved in accordance with the present invention in that two undulated or similarly shaped plates are combined into plate units in such a manner that wave trough rests on wave trough and wave crest on wave crest so that in the one direction flow paths, closed in themselves, result for the one medium, for example for the combustion air of an internal combustion engine, and that alternatingly and sequentially the individual plate units are mutually displaced by a halfwave-phase and are arranged to each other with an internal spacing so that between the individual plate units undulated flow paths extending in the other direction result for the other medium, for example for the exhaust gas of an internal combustion engine, which are lateral! limited by a further structural part or further individual structural parts.

As a further development of the present invention, the lateral limitation for the undulated fiow paths extending in the other direction takes place by similarly undulated terminal strips or bars which are provided with straight end sections having portions bent back parallel, whose height corresponds to the amplitude plus the sheet metal thickness of the undulated plates whereby the end surfaces of the bent-back portions abut form-lockingly against the undulations of the plates.

In order to render the heat-exchanger insensitive with respect to the high temperatures prevailing at the exhaust gas inlet, it is furthermore proposed, according to the present invention, to construct the flow paths for the air, which extend transversely at the exhaust gas inlet, as relatively thick-walled pipes.

For increasing the form-rigidity of the heat-exchanger, also the flow paths for the exhaust gas, which extend transversely at the exhaust gas outlet may be constituted by special, relatively thick-walled pipes.

With a view to an economic assembly of the individual parts of the heat-exchanger, all mutual contact surfaces are connected with each other according to the present invention by insertion of solder, in the form of soldering pastes or soldering foils, and by subsequent oven-soldering.

The present invention assures a structurally simple and operationally reliable construction of the heat-exchanger. These advantages are achieved by the particular configuration, assembly and arrangement of the individual plates whereby also an economic manufacture of the heat-exchanger as regards the connection of the individual structural parts is possible by the use of oven-soldering. Furthermore, a high heat-transfer coeflicient is assured by the undulated configuration of the flow paths for the one medium, especially the hot exhaust gases. The flow volume of both media participating in the heat exchange and the heat-exchange etficiency can be determined in a simple manner by varying the amplitude of the undulation of the plates and by the division (frequency) of the waves without changes of the basic construction of the heat-exchanger. In contradistinction to heat-exchangers with flat plates and thick-walled lateral terminal bars, in which the danger of crack formation is correspondingly relatively large, this danger is considerably reduced according to the present invention by the undulation of the plates. By embossments or indentations in the individual plates on the exhaust gas side, which in relation to two adjacent plates are located mutually opposite one another and have such a depth that the bottoms thereof mutually contact each other, not only an internal reinforcement and strengthening of the heatexchanger is achieved but also the heat-exchange eflrciency is increased. Conversely with undulated plates these indentations do not require different thicknesses of the lateral terminal strips or bars since the cross section of the flow paths, as mentioned above, can be realized by varying the wave amplitude and wave frequency in a simple manner.

Accordingly, it is an object of the present invention to provide a recuperative heat-exchanger which is sim ple in construction, reliable in operation, and effectively eliminates the drawbacks encountered with the prior art constructions.

Another object of the present invention resides in a heat-exchanger of the type described above in which the heat-exchanging surfaces are enlarged without requiring difficult structural parts to assure the mutual spacings of the various plates.

A further object of the present invention resides in a recuperative heat-exchanger in which the danger of crack formulation in the plates as a result of heat stresses is greatly reduced.

Still another object of the present invention resides in a recuperative heat-exchanger in which the requirement for different volumes for the media participating in the heat-exchange can be readily satisfied without complicated constructions.

A still further object of the present invention resides in a recuperative heat-exchanger which is not only simple and inexpensive in construction, but which can also be manufactured and assembled in a particularly simplified manner.

Another object of the present invention resides in a heat-exchanger which is relatively insensitive to prevailing, very high temperatures of the medium or media. These and other objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein:

FIGURE 1 is a perspective view of a portion of a heat-exchanger in accordance with the present invention;

FIGURE 2 is a cross-sectional view, on a reduced scale, taken along line II-II of FIGURE 1; and

FIGURE 3 is a partial elevational view on a heat-exchanger in the direction of the arrow X of FIGURE L with special pipes for the air provided on the exhaust gas inlet and outlet side of the heat-exchanger.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, the heat-exchanging mass of the heatexchanger of the present invention consists of many undulated plates whereby two plates 11 and 12 each are combined into a plate unit generally designated by reference numeral 13, and more particularly in such a manner that wave trough is aligned with wave trough and wave crest with wave crest so that individual flow paths 14, closed in themselves, result for one medium participating in the heat-exchange, preferably for the combustion air L of an internal combustion engine. The individual plate units 13 are offset or displaced alternately and sequentially by half a wave-phase with respect to each other and are arranged to each other with an internal distance or spacing a so that between the individual plate units 13, undulated flow paths 15 result for the other medium participating in the heat-exchange, and more particularly for the hot exhaust gas G which flow paths 15 extend in the other direction. The lateral boundary of the undulated flow paths 15 takes place by similarly undulated terminal strips or bars 16 which are provided with rectilinear end parts 17 having parallel bent-back portions 18 whose height h corresponds to the amplitude plus the sheet metal thickness of the undulated plate 11 or 12, whereby the end surfaces 19 of the bent-back portions 18 abut form-lockingly at the undulations of the plates 11 and 12.

As is shown in FIGURE 2, the individual plates 11 and 12, in order to increase the heat-exchange efiiciency, are provided with indentations 20 which may be arranged distributed at random over the surfaces on the air side, i.e., within the flow paths 14, whereas the indentations 21 on the side of the exhaust gas, i.e., within the flow paths 15, are so arranged and constructed in relation to the individual adjacent plates 11 and 12 that they are disposed mutually facing each other and have such a depth that the bottoms thereof contact each other for the mutual support.

A higher base bar or strip 22 (FIGURE 1) is provided as the lower terminal bar. During the assembly, the individual terminal bars 22 and 16 are threaded into U- shaped sectional members 23 with interposition of the plate units 13. The rigid connection of all individual structural parts of the heat-exchanger takes place at all mutual contact places by the interposition of solder, in the form solder paste or solder foil, by oven-soldering. After the soldering operation takes place the welding op eration of the supply channels to the heat-exchanger for the individual media participating in the heat-exchange.

As can be seen from FIGURE 3, the flow paths 14a for the air L, which extend transversely at the gas inlet, are constructed as special, relatively thick-walled pipes 24a. Also the flow paths 14b for the air L, which extend transversely at the exhaust gas outlet, may be formed by special, relatively strong-walled pipes 24b. The reasons therefor have been indicated already hereinabove.

While I have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and I therefore do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompased by the scope of the appended claims.

I claim:

1. A recuperative heat-exchanger the heat-exchanging mass of which is formed by individual plates defining therebetween mutually crossing flow paths, the flow paths extending in one direction being traversed by a relatively hot fluid medium, and the flow paths extending in the other direction being traversed by a relatively cooler fluid medium, wherein the improvement comprises a plurality of plates of approximately undulated shape, two plates each being combined into a plate unit in such a manner that a wave trough of one plate is aligned approximately with a wave trough of the other plate and a wave crest of one with a wave crest of the other, forming fully enclosed flow paths for one medium in one direction, the individual plate units being oflset alternately and sequentially with respect to one another by approximately half a wavephase and being spaced from one another so as to define approximately undulated flow paths for the other medium extending between the individual plate units in the other direction, and further structural means for laterally limiting the undulated flow paths, wherein said further structural means includes similarly undulated terminal bars having substantially rectilinear end sections provided with parallel bent-back portions, the height of said bent-back portions corresponding to the amplitude of a wave formed by a plate plus the thickness of the undulated plates, and the end surfaces of the bent-back portions abutting formlockingly at the undulations of the plates.

2. A heat-exchanger according to claim 1, wherein the flow paths for the one medium extending transversely at the inlet for the other medium are constructed as separate, relatively thick-walled pipes.

3. A heat-exchanger according to claim 2, wherein the flow paths for the one medium extending in the transverse direction at the outlet for the other medium are constructed as separate, relatively thick-walled pipes.

4. A heat-exchanger according to claim 3, wherein substantially all mutual contact spaces of all structural elements of the heat-exchanger are securely connected with each other by solder joints.

5. A heat-exchanger according to claim 4, wherein the individual undulated plates are provided with individual indentation means in the direction toward the side of the other medium, which are located mutually opposite in relation to adjacent plates and have such a depth that the bottoms thereof contact each other for the mutual support.

6. A heat-exchanger according to claim 1, wherein the flow paths for the one medium extending transversely at the inlet for the other medium are constructed as separate, relatively thick-walled pipes.

7. A heat-exchanger according to claim 6, wherein the flow paths for the one medium extending in the transverse direction at the outlet for the other medium are constructed as separate, relatively thick-walled pipes.

8. A heat-exchanger according to claim 6, wherein substantially all mutual contact spaces of all structural elements of the heat-exchanger are securely connected with each other by solder joints.

9. A heat-exchanger according to claim 8, wherein the individual undulated plates are provided with individual indentation means in the direction toward the side of the other medium, which are located mutually opposite in relation to adjacent plates and have such a depth that the bottoms thereof contact each other for the mutual support.

10. A heat-exchanger according to claim 6, wherein the flow paths for the one medium extending in the transverse direction at the outlet for the other medium are constructed as separate, relatively thick-walled pipes.

11. A heat-exchanger according to claim 1, wherein substantially all mutual contact spaces of all structural elements of the heat-exchanger are securely connected with each other by solder joints.

12. A heat-exchanger according to claim 1, wherein the individual undulated plates are provided with individual indentation means in the direction toward the side of the other medium, which are located mutually opposite in relation to adjacent plates and have such a depth that the bottoms thereof contact each other for the mutual support.

References Cited UNITED STATES PATENTS 1,910,486 5/1933 Wagner 165-l65 X 2,959,401 11/1960 Burton 165-166 1,775,103 9/1930 Hume 165166 2,462,421 2/1949 Pitt ll66 X 2,566,928 9/1951 Carter 166 FOREIGN PATENTS 541,415 10/1955 Belgium.

2,543 1897 Great Britain.

ROBERT A. OLEARY, Primary Examiner T. W. ST REULE, Assistant Examiner 

